U.S. patent number 5,441,593 [Application Number 08/323,185] was granted by the patent office on 1995-08-15 for fabrication of ink fill slots in thermal ink-jet printheads utilizing chemical micromachining.
This patent grant is currently assigned to Hewlett-Packard Corporation. Invention is credited to Kit C. Baughman, Jeffrey A. Kahn, Paul H. McClelland, Ellen R. Tappon, Kenneth E. Trueba.
United States Patent |
5,441,593 |
Baughman , et al. |
August 15, 1995 |
Fabrication of ink fill slots in thermal ink-jet printheads
utilizing chemical micromachining
Abstract
An ink fill slot can be precisely manufactured in a substrate
utilizing photolithographic techniques with chemical etching,
plasma etching, or a combination thereof. These methods may be used
in conjunction with laser ablation, mechanical abrasion, or
electromechanical machining to remove additional substrate material
in desired areas. The ink fill slots are appropriately configured
to provide the requisite volume of ink at increasingly higher
frequency of operation of the printhead by means of an extended
portion that results in a reduced shelf length and thus reduced
fluid impedance imparted to the ink. The extended portion is
precisely etched to controllably align it with other elements of
the printhead.
Inventors: |
Baughman; Kit C. (Corvallis,
OR), Kahn; Jeffrey A. (Corvallis, OR), McClelland; Paul
H. (Monmouth, OR), Trueba; Kenneth E. (Corvallis,
OR), Tappon; Ellen R. (Corvallis, OR) |
Assignee: |
Hewlett-Packard Corporation
(Palo Alto, CA)
|
Family
ID: |
21735887 |
Appl.
No.: |
08/323,185 |
Filed: |
October 14, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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9151 |
Jan 25, 1993 |
5387314 |
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Current U.S.
Class: |
216/27; 216/41;
216/52; 216/99; 347/65 |
Current CPC
Class: |
B41J
2/1404 (20130101); B41J 2/14145 (20130101); B41J
2/1603 (20130101); B41J 2/1628 (20130101); B41J
2/1629 (20130101); B41J 2/1631 (20130101); B41J
2/1632 (20130101); B41J 2/1634 (20130101) |
Current International
Class: |
B41J
2/14 (20060101); B41J 2/16 (20060101); G01D
015/00 (); B44C 001/22 () |
Field of
Search: |
;156/643,644,645,647,653,656,657,659.1,661.1,662,651 ;346/14R
;216/27,41,52,99 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0314486 |
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May 1989 |
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EP |
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0401996 |
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Dec 1990 |
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EP |
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Other References
K E. Bean, "Anisotropic Etching of Silicon", in IEEE Transactions
On Electron Devices, vol. ED-25, No. 10, pp. 1185-1192 (Oct. 1978).
.
K. L. Petersen, "Silicon As A Mechanical Material", in Proceedings
Of The IEEE, vol. 70, No. 5, pp. 420-457 May (1982). .
E. Bassous, "Fabrication Of Novel Three-Dimensional Microstructures
By The Anisotropic Etching Of (100) and (110) Silicon", in IEEE
Transactions On Electron Devices, vol. ED-25, No. 10, pp. 1178-1185
(Oct. 1978)..
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Primary Examiner: Powell; William
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION(S)
This is a continuation of application Ser. No. 08/009,151 filed on
Jan. 25, 1993, now U.S. Pat. No. 5,387,314.
The present application is related to U.S. Pat. No. 5,317,346
entitled "Compound Ink Feed Slot" and assigned to the same assignee
as the present application. The present application is also related
to U.S. Pat. No. 5,308,442 entitled "Anisotropically Etched Ink
Feed Slot in Silicon" and assigned to the same assignee as the
present application.
Claims
What is claimed is:
1. A method for fabricating ink fill slots in thermal ink jet
printheads, comprising the steps of:
(a) providing a crystalline substrate having two opposed,
substantially parallel major surfaces, defining a primary surface
and a secondary surface;
(b) forming an insulating dielectric layer on both said
surfaces;
(c) patterning said insulating dielectric layer on said secondary
surface to expose underlying portions of said crystalline
substrate;
(d) etching part way through said crystalline substrate with an
anisotropic etchant at said exposed portions to thereby form a
portion of said ink fill slot;
(e) forming and defining thin film resistor elements and conductive
traces on said insulating dielectric layer on said primary surface;
and
(f) etching from said primary surface to connect with said portion
of said ink fill slot to thereby completely form said ink fill
slot.
2. The method of claim 1 wherein said step of etching through said
primary surface to completely form said ink fill slot is done by at
least one of anisotropic and isotropic etching.
3. The method of claim 2 wherein said isotropic etching step is
done by at least one of wet chemical etching and dry plasma
etching.
4. A method for fabricating ink fill slots in thermal ink jet
printheads, comprising the steps of:
(a) providing a crystalline substrate having two opposed,
substantially parallel major surfaces, defining a primary surface
and a secondary surface;
(b) forming an insulating dielectric layer on said primary
surface;
(c) forming and defining thin film resistor heaters and conductive
traces on said insulating dielectric layer on said primary
surface;
(d) patterning said insulating dielectric layer on said primary
surface to expose underlying portions of said crystalline
substrate;
(e) etching part way through said crystalline substrate with an
etchant at said exposed portions to thereby form a portion of said
ink fill slot; and
(f) micromachining from said secondary surface to connect with said
portion of said ink fill slot to thereby completely form said ink
fill slot.
5. The method of claim 4 further comprising the step of providing a
passivating dielectric layer covering said insulating dielectric
layer and said thin film resistor heaters and conductive
traces.
6. The method of claim 5 wherein said step of micromachining from
said secondary surface is done by one of mechanical abrasion, laser
ablation, or electromechanical machining.
7. The method of claim 6 wherein said step of mechanical abrasion
is done by sand-blasting.
Description
TECHNICAL FIELD
The present invention relates to thermal ink-jet printers, and,
more particularly, to an improved printhead structure for
introducing ink into the firing chambers.
BACKGROUND ART
In the art of thermal ink-jet printing, it is known to provide a
plurality of electrically resistive elements on a common substrate
for the purpose of heating a corresponding plurality of ink volumes
contained in adjacent ink reservoirs leading to the ink ejection
and printing process. Using such an arrangement, the adjacent ink
reservoirs are typically provided as cavities in a barrier layer
attached to the substrate for properly isolating mechanical energy
to predefined volumes of ink. The mechanical energy results from
the conversion of electrical energy supplied to the resistive
elements which creates a rapidly expanding vapor bubble in the ink
above the resistive elements. Also, a plurality of ink ejection
orifices are provided above these cavities in a nozzle plate and
provide exit paths for ink during the printing process.
In the operation of thermal ink-jet printheads, it is necessary to
provide a flow of ink to the thermal, or resistive, element causing
ink drop ejection. This has been accomplished by manufacturing ink
fill channels, or slots, in the substrate, ink barrier, or nozzle
plate.
Prior methods of forming ink fill slots have involved many
time-consuming operations, resulting in variable geometries,
requiring precise mechanical alignment of parts, and typically
could be performed on single substrates only. These disadvantages
make prior methods less desirable than the herein described
invention.
For example, while sandblasting has been used effectively, it is
difficult to create ink slot features that are relatively uniform
and free of contamination. Photolithography quality depends greatly
on surface conditions and flatness, both of which are very much
affected by sandblasting.
Further, at higher frequencies of operation, the prior art methods
of forming ink slots provide channels that simply do not have the
capacity to adequately respond to ink volume demands.
Fabrication of silicon structures for ink-jet printing are known;
see, e.g., U.S. Pat. Nos. 4,863,560, 4,899,181, 4,875,968,
4,612,554, 4,601,777 (and its reissue RE 32,572), 4,899,178,
4,851,371, 4,638,337, and 4,829,324. These patents are all directed
to the so-called "side-shooter" ink-jet printhead configuration.
However, the fluid dynamical considerations are completely
different than for a "top-shooter" (or "roof-shooter")
configuration, to which the present invention applies, and
consequently, these patents have no bearing on the present
invention.
U.S. Pat. No. 4,789,425 is directed to the "roof-shooter"
configuration. However, although this patent employs anisotropic
etching of the substrate to form ink feed channels, it fails to
address the issue of how to supply the volume of ink required at
higher frequencies of operation. Further, there is no teaching of
control of geometry, pen speed, or specific hydraulic damping
control. Specifically, this reference fails to address the issue of
precisely matching the fluid impedance of every functional nozzle
so that they all behave the same.
A need remains to provide a process for fabricating ink fill slots
in thermal ink-jet print-heads in which the fluid impedance of
every functional nozzle is precisely matched.
DISCLOSURE OF INVENTION
It is an advantage of the present invention to provide ink fill
slots with a minimum of fabrication steps in a batch processing
mode.
It is another advantage of the invention to provide precise control
of geometry and alignment of the ink fill slots to permit precise
matching of fluid impedances of each nozzle.
It is a still further advantage of the invention to provide ink
fill slots appropriately configured to provide the requisite volume
of ink at increasingly higher frequency of operation, up to at
least 14 kHz.
In accordance with the invention, an ink fill slot can be precisely
manufactured in a substrate utilizing photolithographic techniques
with chemical etching, plasma etching, or a combination thereof.
These methods may be used in conjunction with laser machining,
mechanical abrasion, electromechanical machining, or conventional
etch to remove additional substrate material in desired areas.
The improved ink-jet printhead of the invention includes a
plurality of ink-propelling thermal elements, each ink-propelling
element disposed in a separate drop ejection chamber defined by
three barrier walls and a fourth side open to a reservoir of ink
common to at least some of the elements, and a plurality of nozzles
comprising orifices disposed in a cover plate in close proximity to
the elements, each orifice operatively associated with an element
for ejecting a quantity of ink normal to the plane defined by each
element and through the orifices toward a print medium in
pre-defined sequences to form alphanumeric characters and graphics
thereon. Ink is supplied to the thermal element from an ink fill
slot by means of an ink feed channel. Each drop ejection chamber
may be provided with a pair of opposed projections formed in walls
in the ink feed channel and separated by a width to cause a
constriction between the plenum and the channel, and each drop
ejection chamber may be further provided with lead-in lobes
disposed between the projections and separating one ink feed
channel from a neighboring ink feed channel. The improvement
comprises forming the ink fill slot and the drop ejection chamber
and associated ink feed channel on one substrate, in which the ink
fill slot is partially formed by anisotropic etching of the
substrate, employing chemical etching. The dimensions of the ink
fill slot relative to the ink feed channel may be precisely
controlled to aid in fluid tuning of the pen.
The ink fill slot. position can be controlled to within about 20
.mu.m of the hydraulic limiting orifice (the area between the
lead-in lobes) and can be modulated in depth as the slot extends to
minimize air bubble trapping.
The frequency of operation of thermal ink-jet pens is dependent
upon the shelf or distance the ink needs to travel from the ink
fill slot to the firing chamber, among other things. At higher
frequencies, this distance, or shelf, must also be fairly tightly
controlled. Through photochemical micromachining, this distance can
be more tightly controlled and placed closer to the firing chamber.
Etching can be from the frontside, backside, or both. A combination
of etch processes can allow a range of profiles of the ink fill
slot and shelf. This process can be used instead of, or in
conjunction with, conventional "mechanical" slotting procedures to
enhance performance or allow batch processing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a resistor situated in a firing
chamber formed from a barrier layer, an ink feed channel
fluidically communicating with the firing chamber, and an ink fill
slot for supplying ink to the ink feed channel, in accordance with
the invention;
FIG. 2a is a top plan view of the configuration depicted in FIG. 1
and including adjacent resistors and ink feed channels, in which
the shelf length is a constant dimension as measured from the
entrance to the ink feed channel;
FIG. 2b is a view similar to that of FIG. 2a, but depicting an
equalized shelf length that follows the contours of the barrier
layer;
FIG. 3 is a top plan view of a portion of a printhead, showing one
embodiment of a plurality of the configurations depicted in FIG.
2A;
FIGS. 4A-4D are cross-sectional views of the resistor configuration
of FIG. 3, showing the results of anisotropic etching of a
<100> oriented silicon substrate;
FIGS. 5A-5D are similar views as FIGS. 4A-4D, but with a
<110> oriented silicon substrate;
FIGS. 6A-6D are cross-sectional views equivalent to FIGS. 4A-4D or
5A-5D in which the ink-feed slot is produced by abrasive or laser
micromachining; and
FIG. 7, on coordinates of pen frequency in Hertz and shelf length
in micrometers, is a plot of the dependence of pen frequency as a
function of shelf length for a specific drop volume case.
BEST MODES FOR CARRYING OUT THE INVENTION
Referring now to the drawings where like numerals of reference
denote like elements throughout, FIG. 1 depicts a printing or drop
ejecting element 10, formed on a substrate 12. FIGS. 2a and 2b
depict three adjacent printing elements 10, while FIG. 3 depicts a
portion of a printhead 13 comprising a plurality of such firing
elements and shows a common ink fill slot 18 providing a supply of
ink thereto. Although FIG. 3 depicts one common configuration of a
plurality of firing elements, namely, two parallel rows of the
firing elements 10 about a common ink fill slot 18, other
configurations employed in thermal ink-jet printing, such as
approximately circular and single row, may also be formed in the
practice of the invention.
Each firing element 10 comprises an ink feed channel 14, with a
resistor 16 situated at one end 14a thereof. The ink feed channel
14 and drop ejection chamber 15 encompassing the resistor 16 on
three sides are formed in a layer 17 which comprises a
photopolymerizable material which is appropriately masked and
etched/developed to form the desired patterned opening.
Ink (not shown) is introduced at the opposite end 14b of the ink
feed channel 14, as indicated by arrow "A", from an ink fill slot,
indicated generally at 18. Associated with the resistor 16 is a
nozzle, or convergent bore, located near the resistor in a nozzle
plate 22. Droplets of ink are ejected through the nozzle (e.g.,
normal to the plane of the resistor 16) upon heating of a quantity
of ink by the resistor.
A pair of opposed projections 24 at the entrance to the ink feed
channel 14 provide a localized constriction, as indicated by the
arrow "B". The purpose of the localized constriction, which is
related to improve the damping of fluid motion of the ink, is more
specifically described in U.S. Pat. No. 4,882,595, and forms no
part of this invention.
Each such printing element 10 comprises the various features set
forth above. Each resistor 16 is seen to be set in a drop ejection
chamber 15 defined by three barrier walls and a fourth side open to
the ink fill slot 18 of ink common to at least some of the elements
10, with a plurality of nozzles 20 comprising orifices disposed in
a cover plate 22 near the resistors 16. Each orifice 20 is thus
seen to be operatively associated with an resistor 16 for ejecting
a quantity of ink normal to the plane defined by that resistor and
through the orifices toward a print medium (not shown) in defined
patterns to form alphanumeric characters and graphics thereon.
Ink is supplied to each element 10 from the ink fill slot 18 by
means of an ink feed channel 14. Each firing element 10 is provided
with a pair of opposed projections 24 formed in walls in the ink
feed channel 14 and separated by a width "B" to cause a
constriction between the ink fill slot 18 and the channel. Each
firing element 10 may be provided with lead-in lobes 24a disposed
between the projections 24 and separating one ink feed channel 14
from a neighboring ink feed channel 14'.
The improvement comprises a precision means of forming the ink fill
slot 18 and associated ink feed channel 14 on one substrate 12. In
the process of the invention, the ink fill slot 18 is extended to
the pair of lead-in lobes 24a of each firing chamber, either at a
constant distance from the entrance to the ink feed channel 14, as
shown in FIG. 2A, or at an equalized distance from the contour
formed by the barrier layer 17, as shown in FIG. 2B. The ink fill
slot 18 is extended by means of extension 18a toward the lead-in
lobes 24a, using precise etching, described in greater detail
below, to controllably align the ink fill slot relative to the
entrance to the ink feed channel 14, indicated at "A".
In FIG. 2A, the extended portion 18a of the ink fill slot 18
terminates at a constant distance from the centerline of the ink
fill slot, very close to the lead-in lobes 24a. Use of precise
etching, described below, permits a shorter shelf length, S.sub.L,
to be formed; this shelf length is shorter than that of a presently
commercially available pen used in Hewlett-Packard's DeskJet.RTM.
printer, which extends to the edge of the ink fill slot 18. The
shorter shelf length permits firing at higher frequencies than
presently commercially available pens. While the fluid impedance of
the pen imparted to the ink is reduced compared to that in the
commercially available pens, thereby resulting in improved
performance, it is not substantially constant from one resistor
heater 16 to the next.
In FIG. 2B, the extended portion 18a of the ink fill slot 18
follows the contour of the barrier wall 17 defining the lead-in
lobes 24a, providing an equalized shelf length S.sub.L. This
equalized shelf length provides a substantially constant fluid
impedance to the ink in the pen, which results in improved pen
performance.
In accordance with the invention, the extended portion 18a of the
ink fill slot 18 is precisely manufactured in a substrate 12
utilizing photolithographic techniques with chemical etching,
plasma etching, or a combination thereof. These methods may be used
in conjunction with laser micromachining, mechanical abrasion, or
electromechanical machining to remove additional substrate material
in desired areas.
Representative substrates for the fabrication of ink fill slots 18
in accordance with the invention comprise single crystal silicon
wafers, commonly used in the microelectronics industry. Silicon
wafers with <100> or <110> crystal orientations are
preferred. Three methods of ink fill slot fabrication consistent
with this invention are detailed below. Typical resultant
structures are shown in FIGS. 4C, 5C, and 6C.
In one embodiment, depicted in FIGS. 4A-D, the following steps are
performed:
1. Mask the silicon wafer 12 to protect areas not to be etched.
Thermally grown oxide 26 is a representative etch mask for
silicon.
2. Photo-define openings in the etch mask using conventional
microelectronics photolithographic procedures to expose the silicon
on the secondary (back) surface to be removed in the desired ink
flow channel areas.
3. Etch part way into the silicon substrate from the back surface
through the exposed areas of the openings to form the ink fill
slots 18, using anisotropic etchants to provide the desired
geometric characteristics of the ink flow channels.
4. Etch into the front surface (a) to connect with the ink fill
slots 18 and (b) to extend the ink fill slots to the entrances of
the ink feed channels formed in the barrier layer 17, forming
portion 18a. The barrier layer 17 and defined drop ejection chamber
15 and ink feed channel 14, along with resistor heater 16 and
associated electrical traces, are formed in separate steps prior to
this step. The etching in this step may be done using any or all of
an isotropic etchant, such as dry (plasma) etching.
FIG. 4D is a cross-sectional view of a final structure in which ink
is fed from the bottom of the substrate 12. In the process depicted
in FIGS. 4A-D, <100> oriented silicon is employed as the
substrate 12. A thin oxide film 26 is formed on both surfaces 12a,
12b of the substrate and is used to define the ink fill slot 18 to
be etched. Alternatively, a thin nitride film, Si.sub.3 N.sub.4,
may be used, alone or in conjunction With the SiO.sub.2 film.
The dielectric 26 on the secondary surface 12b is patterned prior
to formation of the ink fill slot 18.
The ink fill slot 18 comprises two portions. The first portion,
18', is formed by anisotropic etching. Since the anisotropic
etching is in <100> silicon, the angle formed is
54.74.degree., as is well-known. An aqueous solution of KOH, in a
ratio of KOH:H.sub.2 O of 2:1, heated to about 85.degree. C. is
used for the anisotropic etching. This etchant etches <100>
silicon at a rate of about 1.6 .mu.m/minute. As is well-known, the
etching action is greatly reduced at a point where the <111>
planes intersect, and the <100> bottom surface no longer
exists.
The anisotropic etching is stopped part way through the silicon
wafer 12, as shown in FIG. 4A. Next, heater resistors 16 (and
electrical traces, or conductors, associated therewith, not shown)
are formed on the front surface 12a of the wafer, as shown in FIG.
4B. The process, which is well-known, comprises forming appropriate
layers and patterning them.
The second portion, 18a, of the ink fill slot 18 is formed by a
combination of isotropic and anisotropic etching, either by wet or
dry processes, from the primary surface 12'. This process etches
through the dielectric layer 26 on the primary surface 12a and into
the silicon wafer 12 to connect with the previously-etched ink fill
slot portion 18'. The resulting structure is shown in FIG. 4C.
Dry etching in a plasma system may be used to define the second
portion 18a. CF.sub.4 may be used, but other plasma etchants are
also available for faster etching of the passivation while still
protecting the silicon surface from overetch.
It is this latter etching step that brings the ink fill slot 18
very close to the ink feed channel 14. The proximity of the ink
fill slot 18 to the ink feed channel 14 permits the printhead to be
very responsive to demands for ink required at high drop ejection
frequencies. Suitable masking is used to form the second portion
18a; this masking may be configured to permit obtaining either the
constant shelf length structure depicted in FIG. 2A or the
equalized shelf length structure depicted in FIG. 2B.
The structure is completed, as depicted in FIG. 4D, by the
formation of the barrier layer 17 and the orifice plate 22 with
nozzles 20 therein.
FIGS. 5A-D represent a similar cross-sectional view of a final
structure in which ink is fed from the bottom of the substrate 12,
which in this case is <110> oriented. Here, anisotropic
etching may be used to etch part way or all the way through the
substrate 10, using the same etchant as for <100>. The only
difference in the process of this embodiment from that depicted in
FIGS. 4A-D is the use of silicon of a different crystallographic
orientation.
In another embodiment, shown in FIGS. 6A-D, the wafer is processed
by known thermal ink-jet processes on the primary surface to form
resistors 16 on the surface of the passivating layer 26. A suitable
photodefined masking layer (not shown) is then applied and imaged,
exposing the area to be precision etched. Examples of such masking
layers include DuPont's PARAD or VACREL and thick positive
photoresist, such as Hoechst's AZ4906. In this case, only the
primary surface, 12a, needs to be protected by the insulating
dielectric layer 26.
Etching is done by well-documented dry processes utilizing CF.sub.4
+O.sub.2, SF.sub.6, or a mixture of fluorocarbon and noble gases to
form portion 18a. The etch profile can be controlled by varying
operating pressure and/or etcher configuration from reactive ion
etching regimes (about 50 to 150 millitorr pressures and about 400
to 1,000 volts effective bias) anisotropic etching to high pressure
planar etch regions (about 340 to 700 millitorr pressure and 0 to
about 100 volts effective bias) isotropic etching or some subtle
and beneficial combination of processes. The main part 18' of the
ink feed slot 18 is then formed by micromachining, such as
mechanical abrasion, e.g., sandblasting, or laser ablation, or
electromechanical machining from the secondary surface 12b.
The barrier layer 17 is generally formed prior to the final
formation of the main part 18', for reasons related to wafer
handling (making the wafer stronger) and parts flow (avoiding
returning the wafer to the clean room for processing).
The frequency limit of a thermal ink-jet pen is limited by
resistance in the flow of ink to the nozzle. Some resistance in ink
flow is necessary to damp meniscus oscillation. However, too much
resistance limits the upper frequency that a pen can operate. Ink
flow resistance (impedance) is intentionally controlled by a gap
adjacent the resistor 16 with a well-defined length and width. This
gap is the ink feed channel 14, and its geometry is described
elsewhere; see, e.g., U.S. Pat. No. 4,882,595, issued to K. E.
Trueba et al and assigned to the same assignee as the present
application. The distance of the resistor 16 from the ink fill slot
18 varies with the firing patterns of the printhead.
An additional component to the impedance is the entrance to the ink
feed channel 14, shown on the drawings at A. The entrance comprises
a thin region between the oriplate 22 and the substrate 12 and its
height is essentially a function of the thickness of the barrier
material 17. This region has high impedance, since its height is
small, and is additive to the well-controlled intentional impedance
of the gap adjacent the resistor.
The distance from the ink fill slot 18 to the entrance to the ink
feed channel 14 is designated the shelf S.sub.L. The effect of the
length of the shelf on pen frequency can be seen in FIG. 7: as the
shelf increases in length, the nozzle frequency decreases. The
substrate 12 is etched in this shelf region to form extension 18a
of the ink fill slot 18, which effectively reduces the shelf length
and increases the cross-sectional area of the entrance to the ink
feed channel 14. As a consequence, the fluid impedance is reduced;
both of the embodiments described above are so treated. In this
manner, all nozzles have a more uniform frequency response. The
advantage of the process of the invention is that the entire pen
can now operate at a uniform higher frequency. In the past, each
nozzle 20 had a different impedance as a function of its shelf
length. With this variable eliminated, all nozzles have
substantially the same impedance, thus tuning is simplified and
when one nozzle is optimized, all nozzles are optimized.
Previously, the pen had to be tuned for worst case nozzles, that
is, the gap had to be tightened so that the nozzles lowest in
impedance (shortest shelf) were not under-damped. Therefore,
nozzles with a larger shelf would have greater impedance and lower
frequency response.
The curve shown in FIG. 7 has been derived from a pen ejecting
droplets of about 130 pl volume. For this pen, a shelf length of
about 10 to 50 .mu.m is preferred for high operating frequency. For
smaller drop volumes, the curves are flatter and faster.
As described earlier, FIGS. 2A and 2B depict the shelf length
(S.sub.L). In the former case, the shelf is at a constant location
on the die and therefore the S.sub.L dimension as measured from the
entrance to the ink feed channel 14 varies somewhat due to resistor
stagger, while in the latter case, the shelf length is equalized,
in that it follows the contours of the barrier layer 17.
Industrial Applicability
The precision etch of the primary surface of the silicon substrate
in combination with the anisotropically etch through the secondary
surface provides improved ink flow characteristics and is expected
to find use in thermal ink-jet printheads. The precision etch may
be done by a variety of isotropic etching processes.
Thus, there has been disclosed the fabrication of ink fill slots in
thermal ink-jet printheads utilizing photochemical micromachining.
It will be apparent to those skilled in this art that various
changes and modifications of an obvious nature may be made without
departing from the spirit of the invention, and all such changes
and modifications are considered to fall within the scope of the
invention, as defined by the appended claims.
* * * * *